The present invention is directed to modifying the surfaces of solid materials and more particularly to the use of polymerizable surfactants for such modifications.
Surface structure and composition determine many of the physical properties and ultimate uses of solid materials. Characteristics such as wetting, friction, electrostatic charging, and adhesion are largely influenced by surface characteristics. Of particular concern are the effects of such surface characteristics on biocompatibility. The alteration of surface characteristics is therefore of special significance in biotechnical applications. Improved methods are accordingly sought for modifying solid surfaces, particularly the surfaces of polymeric objects.
Random, grafted, polymerized surfactants have been used to modify the surfaces of hydrophobic polymers by the adsorption of the surfactant onto the surfaces of polymeric objects from an aqueous dispersion. Lee, J. H., Interactions of PEO-Containing Polymeric Surfactants With Hydrophobic Surfaces, The University of Utah (1988)(hereinafter "Lee"). Lee--particularly concerned with reducing the absorption of blood plasma proteins on hydrophobic surfaces--teaches the synthesis of polymeric surfactants by random free radical copolymerization of a hydrophobic methacrylate (hexyl methacrylate or lauryl methacrylate), a hydrophilic methacrylate (polyethylene oxide methacrylate), and methyl methacrylate.
Akashi, M., et al., "Graft Copolymers Having Hydrophobic Backbone and Hydrophilic Branches. IV. A Copolymerization Study of Water-Soluble Oligovinylpyrrolidone Macromonomers," J. Polymer Sci.: Part A: Polymer Chemistry, Vol. 27, pp. 3521-3530 (1989)(hereinafter "Akashi") teaches amphiphiles prepared by random free radical copolymerization of carboxyl group-terminated oligovinylpyrrodidone with methyl methacrylate or styrene. Syntheses of vinylphenyl-terminated and methacryloyl-terminated oligovinylpyrrolidone macromonomers are described.
Polymerizable surfactants have been used to modify the properties of polymers in aqueous solution. For example, Schulz, et al., "Copolymers of Acrylamide and Surfactant Macromonomers: Synthesis and Solution Properties," Polymer, Vol. 28, pp. 2110-2115 (Nov., 1987)(hereinafter "Schulz") describes macromonomer surfactants wherein the surfactant character is achieved by the addition of a small hydrophobic functionality (e.g., nonylphenol) to a water-soluble polyethylene oxide chain. Related materials and methods are disclosed in U.S. Pat. No. 4,075,411.
Polymerizable surfactants have also been used to modify the surface properties of solids. One class of materials used for this purpose are lipids (non-polymeric materials) which are rendered polymerizable by the addition of various functionalities such as methacrylate groups [Ringsdorf, H., et al., "Hydrophilic Spacer Groups in Polymerizable Lipids: Formation of Biomembrane Models form Bulk Polymerized Lipids," J. Am. Chem. Soc., Vol. 107, pp. 4134-4141 (1985)] and various vinyl groups [Ringsdorf, H., et al., "Saturated and Polymerizable Amphiphiles with Fluorocarbon Chains. Investigation in Monolayers and Liposomes," J. Am. Chem. Soc., Vol. 106, pp. 7687-7692 (1984)]. These polymerizable lipid surfactants have been used to prepare liposomes used in the formation and stabilization of biomembrane models (often referred to as polymeric liposomes).
Polyfunctional polymerizable surfactants have also been used in coatings to modify the surface properties of polymeric objects. European Patent Publication No. 153,133 (hereinafter "Regen"). Preferred polymerizable surfactants taught by Regen are polyfunctional lipids. Regen teaches that monofunctional polymerizable surfactants are ineffective for modifying surfaces of polymeric objects. Other polyfunctional polymerizable surfactants are disclosed in U.S. Pat. No. 3,541,138.
An object of Regen was to overcome the limitations of Langmuir-Blodgett processes, especially when applied to more complex surface topographies. Polymerizable surfactants have of course been employed in Langmuir-Blodgett films. These multilayer surfactant assemblies are exploited in microlithography and other opto-electronic systems. Fendler, J.H., "Polymerized Monolayers from a Styrene Functionalized Surfactant," Colloids and Surfaces, Vol. 35, pp. 343-351 (1989).
Contact lenses are conventionally produced by one of three general techniques--lathing, static casting, and spin casting. Combinations are also known. For example, semi-finished buttons (having one final lens surface) may be formed by static or spin casting and the second lens surface may be produced by lathing. Static and spin casting have the advantage of producing lenses with fewer processing steps than lathing. In either of the molding techniques, the anterior and posterior surfaces of the lens may be formed in one step. Static casting does this by providing two mold surfaces; spin casting does this by providing a mold surface to form the anterior surface and by using the forces generated by spinning liquid monomer to form the posterior surface.
One of the challenges faced when producing lenses by molding is achieving release of the lenses from the molds without damaging the lens surfaces. The phenomenon of lens adherence is a consequence of chemical interactions between mold surfaces and monomer mixtures during polymerization. Among the proposals to meet this challenge is U.S. Pat. No. 4,534,916, which teaches adding (nonpolymerizable) surfactants to the monomer mix. The surfactant addition is reported to improve the surface quality of lenses by decreasing the number of surface defects resulting from mold release (especially of xerogel lenses).
The '916 patent seeks improved surface quality by reducing lens damage during demolding. Others have sought to improve surface quality more directly--by surface modifications. For example, U.S. Pat. No. 4,546,123 teaches covalent attachment of (nonpolymerizable) surfactant molecules to a hydrogel lens surface.
The macromonomer technique for preparing graft copolymers of controlled architecture is well known. Macromonomers or macromers are polymers of molecular weight ranging from the hundreds to tens of thousands, with one of the end groups functionalized to enter into further polymerization. Milkovich, Chiang and Schultz demonstrated the synthesis and applications of a variety of macromers. R. Milkovich, M.T. Chiang, U.S. Pat. No. 3,842,050 (1974); Schultz, G. O. and Milkovich, R., J. App. Polym. Sci., 27, 4773 (1982); Schultz, G. O. & Milkovich, R., J. Polym. Sci. Polym. Chem. Ed., 22, 1633 (1984).
Yamashita, Y.; "Synthesis and Application of Fluorine Containing Graftcopolymers," Polymer Bull., 335-340 (1981); "Synthesis and Characterization of Functional Graft Copolymers by Macromonomer Technique", J. Appl. Polym. Sci., 36, 193-199 (1981); "Synthesis of N-Hydroxyethyl-N-Methylmethacrylamide and Its Use in the Macromonomer Synthesis", J. Polym. Sci., Polym. Letters Ed., 19, 629-636 (1981); (hereinafter "Yamashita") teaches a method of making macromers and the use of macromers to make graft copolymers. Yamashita used free radical polymerization in the presence of an effective chain transfer agent which controlled the molecular weight of the final macromer and also provided a functional end group. Thioglycolic acid, for example, is an effective chain transfer agent which provides a carboxylic acid functional end group. The end group can subsequently be reacted with, e.g., glycidyl methacrylate to give a terminal methacrylate polymerizable group. Yamashita used macromers of MMA to prepare graft copolymers of fluoroalkyl acrylates with polyMMA grafts. Yamashita does not teach the synthesis of polymerizable surfactants by the macromonomer technique.